System for supplying hot dry compressed air



July 3, 1962 G. w. HEINECKE SYSTEM FOR SUPPLYING HOT DRY coMPREssED AIR Filed ont. 26. 1959 N ...WQ

INVENTOR. Gasal/ W. #5A/ECKE United States Patent fice 3,041,842 Patented July 3, 1962 3,041,842 SYSTEM FOR SUPPLYKNG HST DRY CMiRESSED Alti. Gustav W. Reinecke, 1317 W. Ramona Road, Alhambra, Calif. Filed Oct. 2.6, 1959, Ser. No. 848,735 6 Claims. (Cl. 62--93l This invention relates to compressed air supply systems and more particularly to an improved system of this type especially designed for supplying hot dry compressed air economically and by the use of a minimum of equipment.

It is common practice today to perform many arduous tasks using compressed air as the power source, pneumatically driven power tools of a wide variety of types, designs and purposes being now in wide scale use. Such tools were developed initially for use in areas where electric power is not readily available or under conditions under which the use of electricity is hazardous. More recently the advantages `and versatility of operations perormable with compressed air are such that pneumatic tools are as cormnon in factories as in remote locations, in open areas, in mines and elsewhere.

lt has long been recognized that moisture unavoidably present in compressed atmospheric air is objectionable to some degree for substantially all applications and, in certain of these, the presence of moisture is intolerable. This is because the moisture condenses within `the air lines and particulaly within the working parts of `the tools themselves. Slugs of water collecting in compressed air lines may be conveyed along the lines at high velocity causing severe hammer, objectionable noise as well as rusting of the `conduit and other fittings, The rust akes off fouling the working parts of the toois land of the control Valves. The presence of water in the working parts of the tools is especially objectionable since it causes rusting, fouling of these parts and necessitates frequent and costly servicing. There are also other operations, as for example, the use of compressed air to operate paint spray guns, where `the presence of the moisture causes spots and the like defects in the painted surface.

Various expedients have been developed for drying air in eorts to avoid `the many disadvantages attending the presence of the moisture in compressed air. A common expedient is the use of a desiccant, the glycols, silica gel, activated carbon, `activated alumina and others being among the more common desiccant agents. These are quite effective in removing the objectionable moisture, but are subject to other disadvantages and shortcomings. For example, the desiccants themselves as well as the equipment required tor their use are expensive. Suitable pro-l vision must be made to reactivate the desiccants after a period of use and stand-by facilities are required for drying the air while saturated desiccant is being reactivated for further use. A further and serious objection for certain uses of compressed air resides in the fact that all known and suitable desiccants `contaminate the air. Such contaminants tend to collect in the air lines and in the working parts of the tools operated thereby causing exl cessive service and maintenance problems and frequent ing by far the major portions of the moisture present in the compressed air. Unfortunately, there still remains objectionable quantities of moisture which are likely to condense as the air expands rapidly to atmospheric pressure while being used to drive various pneumatic tools. Such residue moisture, though small in quantity, is nevertheless sufficient to raise serious problems of the type referred to above.

According to this invention the small quantity of residue moisture remaining after evaporative cooling is removed by sharply lowering the air temperature by means of a mechanical refrigeration system. In this manner the temperature of the compressed air is lowered below the dewpoint of the moisture and suiciently to remove substantially all remaining moisture. Thereafter, the dry air is preferably further compressed to a desired operating pressure and is then conducted to `a point of use in heat insulating distributing ducts in order `that the available heat of compression may be utilized advantageously to operate tools.

By use of the expedients just refeired to, by far the greater bulk of the heat of `condensation of moisture in the compressed air is dissipated to the ambient air and to water circulating through the evaporative cooling tower, the major expense involved being the power involved in circulating the ambient cooling air through the 4tower and the value of the inconsequential amount of water lost by evaporation while being circulated through the tower. The small amount of moisture remaining in the cornpressed air is then `condensed as by heat exchange with a small capacity mechanical refrigeration system requiring a proportionately small power input. For example, in an air conditioning system according to this invention whereing one thousand cubic feet of air per minute `are to be compressed to a pressure of one hundred twelve p.s.i.a., it is feasible and practicable to remove fifty pounds of water per hour by the evaporative cooler leaving three pounds per hour to be removed by mechanical refrigeration apparatus. A refrigeration system having a capacity of three tons is entirely adequate for this purpose. As will be appreciated, refrigeration apparatus having many times this capacity would be required if all the condensate were to be removed by refrigeration alone.

Accordingly, it is a primary object of the present invention to provide an improved, more effective and efficient and economical system for continously drying large volumes of compressed air.

Another object `of the invention is the provision of an improved and superior system for continuously supplying hot dry compressed air for various uses including more particularly pneumatically operated tools.

More specicaliy, it is an object of the invention to provide means partially to compress atmospheric air and then to remove the major portion of moisture present by condensation in an evaporative cooler, and for thereafter passing the substantially dried air in heat exchange with the evaporator of a mechanical refrigerator to remove substantially all remaining moisture and thereafter further compressing the dried air and supplying the same while still hot to a tool to be operated thereby.

Another object ci the invention is the provision of an economical system for supplying hot dry compressed air wherein atmospheric air is compressed in stages while being cooled below the dewpoint between stages by evaporative cooling and then lowering the temperature sharply prior to being finally compressed by passing the substantially dry air into heat exchange with the evaporator of a mechanical refrigeration system.

These and other more speciic objects will appear upon reading the following specification and claims and upon considering in connection therewith the attached drawing to which they relate.

Referring now to the drawing in which preferred embodiments of the invention are illustrated:

FIGURE l is a schematic showing of one preferred ernbodiment of the invention; and

FIGURE 2 is a schematic showing of a second preferred embodiment of the invention.

Referring now more particularly to FIGURE l, there is shown schematically a system designated generally lt for compressing and drying air. This system comprises a compresor 11 driven in any convenient manner and having a first stage 12 and a second stage 13. lt will be understood by those familiar with the art that though both compressor stages are indicated as being of the same size, the second stage cylinder 13 will normally be of smaller volumetric capacity than rst stage `12. Atmospheric air to be compressed and dried enters first stage i2 through an inlet conduit 15 and is discharged partially compressed through a conduit 116 leading into a heat exchange coil 17 suitably disposed within an evaporative cooling tower 18 of generally conventional design. A motor driven fan 19 draws atmospheric air inwardly through louvered openings Ztl at the lower end of the tower and upwardly through the downwardly falling water spray and is discharged upwardly through tiue 21. Cool water from the cooler basin 23 is delivered by a pump 29 to a spray head 22 across the top of tower 18 and is sprayed downwardly in counterflow to the rising air. Evaporative cooler 18 operates in known manner to dissipate heat of compression and heat of condensation of the moisture present therein in accordance with well known principles as portions of the falling water evaporate into the air circulating through the cooling tower. The cooling effect from the latent heat of vaporization of the falling water spray cools the compressed air owing through heat exchange coil 17 and condenses moisture therefrom. Condensate separating out of the compressed air in heat exchanger 17 flows through conduit 24 into water separator 25 from which it may be withdrawn through drain pipe 26 by means of a conventional automatic discharge device 27. It will be understood that drain pipe 26 may discharge into a pressurized storage tank or other appropriate facility by which the water may be removed without loss of compressed air,

Substantially dry compressed air present in the top of seapartor 25 then passes through conduit 3tlinto a heat exchanger 31 where it is further sharply cooled by heat exchange with refrigerant changing `from liquid to vapor within chamber 32 forming the evaporator of a closed circuit mechanical refrigeration system designated generally 35. It is pointed out that refrigeration system 35 includes a compressor 36 which receives refrigerant vapor from chamber 32 through an intake conduit 37. This vapor is compressed and delivered through a conduit 3S opening into the top of a condenser 39 where it liqueties. The liquid refrigerant draining therefrom passes into a suitable receiver 4@ from which it flows through a conduit 41 into evaporator chamber 32, there being present I in conduit 41 a suitable restrictor for separating the high pressure side of the refrigeration circuit from the low pressure return side represented by conduit 37.

The evaporation of the liquid refrigerant within evaporator 32 lowers the temperature of the substantially dry -air flowing in conduit 30 causing the remaining moisture to fall below its dewpoint temperature. The condensate and air then ow into a water separator 44 similar to separator 25. The condensate collects in the bottom of this chamber and may be withdrawn through an automatic discharge device 46 and a drain conduit 45 similar to conduit 26 and device 27. The cold substantially moisture-free compressed air discharging from the top of sepa- /rator 44 is conducted by a conduit 47 into second stage d3 with hot dry compressed air is a heat insulated distributing manifold 51. In this manner the hot air is conducted through a flexible hose 52 into the operating chamber of any suitable pneumatically operated tool, such as that generally designated 53. There the hot dry air is allowed to expand to substantially atmospheric pressure while being used to operate the tool or to project a fiuent material such as paint through a spray nozzle.

The two stages of compressor 11 are desirably cooled in larger capacity systems to prevent excessive heat rise. Such cooling may be effected in the illustrated system by a closed water cooling circuit 60 which conducts hot water from the upper ends of cooling jackets 61 surrounding the compressor stages through conduit 62 into the upper end of heat exchange coil 63 located within evaporative cooler 18. The cool water discharging from coil 63 iiows through conduit 64 into water circulating pump 65 from which it is discharged into conduits 66 for delivery into the lower ends of cooling jackets 61.

A further and important feature of the described air drying system comprises a bypass conduit 7i) having one end 71 opening into the hot compressed air Conduit 16 adjacent its point of connection with heat exchanger 17 and its other end 72 discharging into conduit 24 in such manner as to prevent drainage of condensate thereinto. Bypass pipe preferably includes a suitable automatic temperature controlled valve 73 which includes an operating thermostat '74 responsive to the temperature of the Compressed air in conduit 24 on the discharge side of air mixer 75. Valve 73 and thermostat 74 will be understood as operable to regulate the proportion of hot compressed air iiowing through heat exchanger 17 and through bypass conduit 70 as to maintain the temperature of the air entering chilling coil 30 substantially uniform despite widely varying conditions of the air being compressed and at evaporative cooler 18.

Considered generally, the purpose of bypass conduit 70 and of its associated thermally actuated valve 73 is to maintain the load imposed on refrigeration system 35 generally uniform notwithstanding wide uctuations in the wet bulb temperature. For example, it is known that mechanical refrigeration systems operate most eifectively `and efficiently under uniform load conditions. Otherwise the refrigeration system tends to hunt and to operate erratically and inefliciently, particularly under low load conditions. However, the heat absorbing load imposed on refrigeration system 35 unavoidably varies over a wide range despite the fact that `a substantial quantity of air may be undergoing compression and drying. Furthermore, it will be understood that the described precise control of the air temperature at the chiller 31 assures that the temperature of the high pressure discharging from the last stage of the compressor and distributed to the plant remains uniform despite widely fluctuating wet bulb temperatures.

The reason for the described wide fluctuation in operating conditions is due largely to variations in the wet bulb temperature prevailing in evaporative cooler 13. If the atmospheric air owing through cooling tower 18 is very humid, a relatively small amount of water evaporates into this air thereby greatly reducing the heat absorbing eiciency and capacity of the cooling tower. This imposes a larger load on the refrigeration system. On the other hand, very dry atmospheric air conditions permits the cooling tower to operate at high efficiency with the result that lthe air issuing from heat exchanger 17 is relatively cool and dry. Under these conditions very little cooling capacity is required of refrigeration apparatus "35 and it tends to go on and oif frequently with the result that its evaporator operates ineliiciently.

These objectionable conditions are avoided by the present invention in that the thermostatic means controlling valve 73 opens under the conditions last enumerated and allows a controlled portion of the moist hot compressed air to flow through conduit 70 without being cooled.

'Ihis relatively Warm moist air merges in conduit 24 with the very dry and cool air issuing from the heat exchanger with the result that uniform cooling capacity is required of heat exchanger 311 and refrigeration system 35 than would be the case wtihout bypass 70. By properly adjusting thermostatically controlled valve 73, it will be understood that the system operates automatically to impose a fairly uniform load on the refrigeration system despite wide variations in the Wet 'bulb temperature and other factors effecting the overall operating conditions.

The following specific values given by way of example will serve to convey a more precise concept of the operating conditions prevailing in the different parts of the described system.

Let it be assumed, for example, that one thousand suction cubic feet per minute of atmospheric air enter conduit of the first stage compressor 12 at 80 F. dry bulb temperature, 14.7 p.s.i.a. and containing 64.5 pounds per hour of Water vapor. This air may be compressed to 41 p.s.i.a. in the first stage and will have a temperature of approximately `300 F. This compressed air may be cooled to 90 F. in heat exchanger 17 of the evaporative cooler, approximately 50.0 pounds of water per hour separating out in separator 25. lf the air is then chilled to 35 to 40 P. in conduit 30 of heat exchanger 31, approximately 3.0 additional pounds of moisture per hour will separate and collect in separator 44.

The dry air may then be further compressed in second `stage 13 of compressor 11 and delivered to distributing manifold 51 under 112 p.s.i.a. and a temperature of 200 F., the residue moisture content being only 11.2 pounds of water per hour.

Under the conditions just described, the evaporative cooler will remove approximately 309,000 B.t.u. per hour, whereas the load imposed on heat exchanger 31 will be relatively inconsequential or approximately 35,600 B.t.u. per hour. The small amount of water vapor remaining in the -hot compressed air entering pneumatic tool 53 will be so small that it will not separate out as moisture during expansion of the air to atmospheric pressure. Accordingly, condensate does not appear in the compressed air distributing system or on any of the working parts of the tool and rust hazard is substantially non-existent.

Referring now to the second embodiment of the invention illustrated in yFIGURE 2, the same or similar reference characters are used to designate the same or similar parts to those described in FIGURE l, but are distinguished Iby the addition of a prime. This embodiment differs from the first `described system primarily in the use of two primary stages of compressor 12', 13', the output of both of which are cooled by separate heat exchange coils Within evaporative cooler 18'. Thus, the hot compresesd -air conduit 16 of first stage 12, passes through a heat exchanger 76 while flowing to the inlet of second stage 13. Heat exchanger 76 is maintained cool by a circulating flow of Water passing through the evaporative heat exchange coil 73 and through heat exchanger 76 by way of conduit 79. The air compressed to 154 p.s.i.a. then flows through conduit 16" into heat exchanger 17 located in the evaporative cooling tower and from there into separator by way of conduit 24'. After the Iair is further dried by heat exchange within coil of heat exchanger 31 of the refrigeration system it passes into water separator 44 and from there through conduit 47 into third stage '77 of compressor 11. There the air is further compressed to 500 p.s.i.a. and delivered to the heat insulated air storage chamber 50 through conduit 48. The hot compressed air then is ready for use and has a temperature of approximately 250 F. and a Water content of approximately 3.42 pounds per hour.

The mode of operation and the conditions prevailing within the second described system will be readily understood from the foregoing description of the closely related rst embodiment and from the values and illustrative specification characteristics listed 0n FGURE 2.

6 From the foregoing, it will be recognized that there has been disclosed a very simple, economical and highly eicient air drying system characterized by the fact that Vby far the major portion of the moisture present in the compressed air is separated out by use of an evaporative cooler. This is accomplished without sacrificing air drying ability since the remaining objectionable quantities of moisture not conveniently removable by evaporative cooling are condensed inexpensively and effectively by use of a small capacity mechanical refrigeration system. Thereafter, the dried air is further compressed to a desired utilization pressure and conducted directly to a point of use while still hot thereby affording further assurances that remaining traces of moisture will not condense While the air is being used to operate a pneumatic tool.

While the particular system for supplying hot dry compressed air herein shown and disclosed in detail is fully capable of attaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design `herein shown other than as defined in the appended claims.

I claim:

1. That method of supplying dry hot pressurized air to pneumatic tools to operate the same without risk of leaving a deposit of water within the tool which method comprises, compressing atmospheric air to a pressure of several atmospheres, cooling said compressed air by heat exchange with water and atmospheric air in an evaporative type water cooling device, separating moisture condensing from said cooled compressed air, passing the cooled partially dried air in heat exchange with refrigerant in a zone out of heat exchange relation with said evaporative cooling device in a zone remote from said evaporative cooling device to condense therefrom substantially all remaining moisture, further compressing the dried air, conveying the hot `dry compressed air into the working chamber of a pneumatic tool and allowing the same to expand toward atmospheric pressure while operating said tool, said method being characterized in that a portion of said compressed air is bypassed around said water cooling device and then merged with the remainder after such remainder has been cooled in said Water cooling device, and varying the portion of the air so bypassed inversely to changes in the wet bulb temperature of the ambient air and in a manner to maint-ain the temperature of the air leaving said Water cooling device within a predetermined range despite fluctuation in the Wet bulb temperature.

i2. That improvement in providing a continuing supply of hot dry compressed air at loW cost and involving utiliz-ation of an evaporative cooler of the air-water type for absorbing the preponderant portion of the heat of condensation of water vapor and of the heat of compression as Well as for removing a relatively minor portion of the aforementioned heats through heat exchange with refrigerant medium held captive in a compression-liquefaction-evaporation circuit; said improvement comprising compressing moisture-bearing -atmospheric air to a first pressure, passing said compressed fair in heat exchange with an evaporative cooler to cool the air below the dewpoint of moisture present therein, separating out condensate, removing the greater portion of the remaining moisture still present by passing the substantially dry compressed air in heat exchange with liquid refrigerant c0nned to a compression-liquefaction-evaporation circuit, and thereafter further compressing the dried air and conducting the resulting hot dry compressed air to a place of use While still hot, and said improvement being further characterized in the provision of adjustable means for bypassing portions of said compresesd air fiowing to said evaporative cooler around said evaporative cooler for the purpose of maintaining the cooling load on said compression-liquefaction-evaporation circuit generally uniform notwithstanding variations in the wet bulb temperature of the atmospheric air.v

3. That improvement dened in claim 2 characterized in that the air undergoing drying is compressed and partially dried in a plurality of stages before being iinally dried by heat exchange With a refrigerant medium and thereafter compressed for delivery to a place of use :as hot dry compressed air.

4. That improvement defined in claim 2 characterized in the provision of means `for bypassing varying quantities of said compressed air past said evaporative cooler and then merging said bypassed air with other compressed air after the same has been cooled in said evaporative cooler, and varying the proportion of the air so bypassed as necessary to maintain the temperature of the merged air substantially uniform despite variations in the Wet bulb temperature of the atmospheric air.

5. That improvement in providing a supply of dry compressed air with minimum expenditure of energy which comprises compressing atmospheric air to a rst pressure, dividing said air into major and minor streams, passing said major stream in heat exchange with evaporatively cooled water to cool the same below the dew -point of moisture present in said air, separating out condensing moisture, merging said major and minor streams in proportions necessary to maintain the temperature of the merged streams substantially uniform, further cooling said merged streams of partially dried compressed vair to remove a substantial portion of the remaining moisture, whereby the subsequent expansion of said dried compressed air in a pneumatically actuated device will not result in the deposition of moisture within said device.

6. That improvement defined in claim 5 further characterized in the compression of said cooled dried compressed air `and the use of the resulting dry compressed air in a pneumatic device while still hot thereby to obtain maximum benet of the energy contained therein with reduced risk of traces of moisture separating within the working parts of said pneumatic device.

References Cited in the le of this patent UNITED STATES PATENTS 1,034,863 Behr Aug. 6, 1912 1,113,682 Patitz Oct. 13, 1914 2,069,269 Perkins Feb. 2, 1937 2,077,315 Ewing Apr. 13, 1937 2,454,883 Olstad Nov. 30, 1948 2,724,249 Gravert Nov. 22, 1955 2,867,988 Brandt Jan. 13, 1959 

